1. Field of the Invention
This invention relates to a sliding nozzle device for a molten metal vessel, and particularly to a mechanism for effecting loading and releasing of surface pressure between a sliding plate and a fixed plate.
2. Description of the Related Art
Sliding nozzle devices provided on various kinds of molten metal vessels are widely used because they enable a flow passage for pouring molten steel or the like from inside a molten metal vessel to be opened and closed as necessary, and they allow the flowrate of molten metal to be controlled accurately.
Among such sliding nozzle devices there are two-plate types, having an upper fixed plate and a lower sliding plate, and three-plate types, having a sliding plate disposed between two fixed plates. Also, to prevent molten steel from getting between these plates, the devices are provided with mechanisms for applying surface pressure to the sliding surfaces of the plates. This surface pressure is set to a value that does not hinder the operation of the sliding nozzle device.
As a surface pressure loading mechanism for applying a surface pressure, coil springs are usually used, and as a mechanism for loading and releasing this surface pressure, a bolt tightening system is employed; however, mechanisms of various other types have also been proposed.
For example, in Japanese Unexamined Patent Publication No. Sho 63-501858, with the object of lightening the work involved in loading a surface pressure, a method of performing surface pressure loading by utilizing a taper of a sliding liner is disclosed.
However, with devices using this method, because a sliding plate must be moved in the direction of the taper of the sliding liner, restrictions are placed on the opening and closing directions of an opening/closing metal frame which holds the plate and restrains the mechanism for doing this on the underside of the molten metal vessel. There are also restrictions on where a cylinder for driving the sliding plate can be mounted, causing problems in removal and fitting thereof.
In Japanese Patent Publication No. Sho 60-15429, there is disclosed a device using a method wherein a coil spring is mounted at the bottom of a cassette, as a surface pressure loading mechanism, and surface pressure is loaded and released by engagement and disengagement of the cassette. However, in a device using this method there is the problem in that the cassette is heavy, requiring a large engaging and disengaging apparatus.
Also, the present inventors have proposed, in Japanese Unexamined Patent Publication No. Hei 6-226430, a device wherein elastic force loading means and a sliding metal frame are disposed between a fixed metal frame and an opening/closing metal frame and surface pressure between plate bricks is loaded and released by moving the opening/closing metal frame, which is itself is connected to and made to slide by a hydraulic cylinder rod for driving the sliding metal frame.
In this device, a recessed portion is provided in the rod of the hydraulic cylinder and a block attached to the opening/closing metal frame is engaged/disengaged with this recess portion. When the block is engaged with the rod, the hydraulic cylinder and the opening/closing metal frame are connected and surface pressure can be loaded or released. When the block is disengaged from the rod and connected to the fixed metal frame, control of the aperture of a pouring hole in a sliding plate becomes possible with the sliding metal frame only.
However, in this device, when the opening/closing metal frame and the hydraulic cylinder are connected, because of variations in joint parts caused by distortion of the block and fluctuations in the hydraulic system due to heat, there are problems in engagement and disengagement of the block. Also, because this block is partly a transmitting force, it must bear several tons of force during loading; consequently manual operation is difficult and the device tends to be large.